Sails for use on small watercraft, such as sailboards, on ice boats or on land vehicles, such as large skateboards, have been developed wherein a mast or spar is secured by a universal-type joint to the sailboard or other type of platform on which the user stands. A generally triangularly shaped sail is mounted on the mast and a wishbone-type boom extends rearwardly from the mast. The sail is disposed between the two curved arms of the boom. The contour of the sail is preset with an outhaul attaching the clew of the sail to the rear of the boom and a downhaul attaching the tack of the sail to the bottom of the mast. Unlike the situation in larger, more sophisticated sailing systems, the steering and control of the sailboard or similar type of craft is accomplished by manipulation of the sail by movement of the boom with the hands of the sailor and by selected placement of the body weight of the sailor relative to the sail and relative to the sailboard or other type of body or platform on which the mast is mounted.
Constructing a sailboard or similar type of craft in the manner described above with simplified rigging is important for minimizing the weight of the craft and also the cost of constructing the craft. In addition, the sailor, who must support the mast to keep it upright, does not have his hands free to adjust or manipulate the typical lines or rigging used on sailboats and other larger, more sophisticated types of sailing vessels. However, the rather simplistic construction of the sails and rigging of conventional sailbaords has heretofor limited the efficiency of the sail as a wind propulsion power source for the sailboard. For example, in known sailboards, a turbulent wake is generated at the juncture between the luff of the sail and the adjacent rear portion of the mast. The wake disturbs the airflow over the sail, thereby reducing the efficiency of the sail. In addition, when the sail is loaded by the wind, the mast not only is bent laterally leeward away from the sailor who is typically located windward of the sail, but also is bent in the aft direction. This bending of the mast imparts a tension load on the sail in the fore and aft direction causing the sail to flatten out and thus assume an inefficient airfoil shape. In addition, with the aft bending of the mast, the clew to head distance is decreased thus allowing the leech to fall off. The resulting flatter sail produces a higher pressure on the leeward side of the luff, thereby causing a more negative aerodynamic moment which decreases the efficiency of the sail.
Accordingly, it is a principal object of the present invention to provide a sailing system for lightweight craft which is of uncomplicated construction and easily and readily controlled, and also in which the sail maintains an efficient aerodynamic shape even when highly loaded.
Means have been suggested for reducing the turbulence generated at the juncture of the sail luff and the mast. For instance, an elongated, nose-shaped sleeve has been engaged over a circular mast and the sail rollably furled within the interior of the sleeve. Although a sleeve of this nature may improve, to some extent, the efficiency of the sail, it undesirably adds a significant amount of weight to the mast. An example of a sailing system using this type of sleeve is disclosed in U.S. Pat. No. 4,149,482.
A further attempt to reduce the turbulent wake caused by the mast has been to construct the mast in an A-shaped cross section with flat, diverging, rearwardly extending sides. The sail is mounted on a mast to permit the luff to move from one side of the mast to the other so that the sail is always positioned on the leeward side of the mast. An obvious drawback of this type of mast is that it is of rather complicated construction. Moreover, turbulence has not been eliminated on the windward side of the mast. An example of this type of mast construction is disclosed by U.S. Pat. No. 3,882,810.
Another effort to reduce the turbulence caused by the mast has been to employ an exterior flap or fairing extending between the mast and the luff of the sail. The fairing typically is substantially rigid and extends the full height of the mast, thus adding considerable weight to the sailing system. Examples of such fairings are disclosed by U.S. Pat. Nos. 2,561,253 and 4,388,888.
A further attempt has been made to lessen the drag and wind resistance caused by the mast by mounting vertical rows of projections on the forward and side surfaces of the mast. The projections are said to separate the air passing around the mast in the form of a turbulent boundary layer which in theory reattaches to the sail in a manner whereby the detached airflow between the mast and sail is less than occurs in a conventional mast. An example of this type of mast construction is disclosed by U.S. Pat. No. 3,866,558.
Efforts also have been expended to selectively vary the draft of the sails of large marine vessels to produce a sail curvature suited to the current sailing conditions. In one such type of sail design, battens are positioned along the intersection of vertically adjacent sail panels. Rollers are mounted on the rearward ends of the battens to receive a leech rope having its upper end connected to the peak of the sail and its lower end spooled on a wench mounted on a boom. The downhaul on the leech rope can be adjusted to change the curvature of the battens. An example of this type of sail construction is disclosed by U.S. Pat. No. 2,561,253.
In another attempt to selectively change the curvature of the sails of rather large sailing vessels, upper and lower arms have been extended rearwardly from upper and lower portions of a mast. The rearward end portions of the upper and lower arms are engaged with intermediate portions of the sail to laterally constrain the sail. Contouring arms are employed to extend transversely outwardly from the upper and lower arms to push against the rear edge of a rather long vane which is engaged over the mast, which vane receives the luff of the sail. The distance that the contouring arms project laterally outwardly from the upper and lower arms controls the camber of the sail. It will be appreciated that a sailing system of this rather complicated construction is not practical for lightweight craft, such as sailboards. An example of this type of sail construction is disclosed by U.S. Pat. No. 4,388,888.
Lightweight sailing craft of the type which the present invention is concerned, such as sailboards, are commonly used for racing and for wave jumping. Footstraps are typically mounted on board sails at fixed locations to anchor the sailor's foot to the board. This is especially important during wave jumping wherein the board may be entirely out of the water and disposed vertically in the air while the sail is oriented horizontally, as is the sailor whose feet are anchored to the board with the footstraps and hands are grasped around the boom. A disadvantage of existing sailboards is that once airborne, the sailor cannot move his feet into other positions, thus often resulting in less than ideal placement of his feet for airborne dynamics. In addition, many individual stationary footstraps are required for the sailboard. Also, conventional booms do not allow for any significant change in the vertical position of the sailor's hands, which, in turn, limits the extent to which the position of the body mass of the sailor can be varied relative to the center of effort of the sail. This is especially significant during wave jumping, wherein if the body can be placed close to the center of effort of the sail, the sailor can achieve level flight by using his sail as the wing, rather than the sailor being pitched forwardly along with the sailboard.
Accordingly, it is also an object of the present invention to provide a sailing system for lightweight craft in which the position of the feet of a sailor standing on a craft can be selectively and conveniently moved relative to the board while maintaining his feet anchored to the board.
It is also an object of the present invention to provide a sailing system for lightweight craft in which the sailor's hands can be placed in variable vertical locations, thereby enabling the sailor to selectively change the position of his body relative to the sail by moving the locations of his hands.